Metal-semiconductor field effect transistor

Basic sketch of an n-channel MESFET

The MESFET ( English metal semiconductor field effect transistor , MESFET) is a barrier layer to the group of field effect transistors ( JFET belonging) electronic semiconductor device . Its structure is similar to an n-channel JFET, but the p-doped gate is replaced by a metal gate. As a result, instead of a pn junction, a rectifying metal-semiconductor junction ( Schottky junction ) is formed, because the metal of the gate now touches the semiconductor material directly.

Due to the very similar structure and functionality, the MeSFET has almost the same properties of an n-channel JFET:

• Like all JFETs, MeSFETs are normally normally-on , i.e. i.e. , at a control voltage of , a drain current flows. ${\displaystyle U_{\mathrm {GS} }=0~\mathrm {V} }$
• The control is carried out by a negative control voltage , which widens the space charge zone of the Schottky junction, which leads to a pinch off of the conductive channel at the threshold voltage , the MeSFET is now blocked. For silicon MeSFETs this would be around 0.3 V. If, on the other hand, GaAs is used as the semiconductor material, the possible voltage is around 0.7 V. ${\displaystyle U_{\mathrm {GS} }}$ ${\displaystyle U_{\mathrm {th} }}$

The advantage of the MeSFET is that, due to the adjacent Schottky junction, the charge carrier mobility in the channel is approximately twice as great as with MOSFETs . This enables higher currents with the same dimensions and higher working frequencies. In addition, in contrast to the JFET, a normally-off variant can be constructed in which the gate is embedded in the substrate.

MeSFETs (especially GaAs MESFETs) are used as microwave transistors in high-frequency amplifiers . They are also used in very fast logic circuits (gigabit logic ).

literature

• Ibrahim M. Abdel-Motaleb, William C. Rutherford, Lawrence Young: GaAs inverted common drain logic (ICDL) and its performance compared with other GaAs logic families. In: Solid-State Electronics. 30, No. 4, 1987, pp. 403-414, doi: 10.1016 / 0038-1101 (87) 90169-9 .